Let it cool to lukewarm and then add the whipping cream and 15 drops green food coloring.
Gather your straws (don’t forget to flex them out) and put them in the container. It’s important that the straws have a tight fit so the jello stays in the straws. For this reason, a 1 liter carton may be better; you will probably get longer worms since there is a tighter fit. If you have a bigger container, a rubber band around the straws is helpful. Or you could just add more straws to fill the container.
Add the gelatin mixture to the straw-filled container and let it set until firm.
There are multiple ways you can remove the worms from the straws. You can roll a rolling pin over the straws and squeeze them out or you can hold the straws over warm water. The worms will slip right out.